(1) I want to know what is the difference between call by value and call by reference in php. PHP works on call by value or call by reference?
(2) And also i want to know that do you mean by $$ sign in php
For example:-
$a = 'name';
$$a = "Paul";
echo $name;
output is Paul
As above example what do u mean by $$ on PHP.
$$a = b; in PHP means "take the value of $a, and set the variable whose name is that value to equal b".
In other words:
$foo = "bar";
$$foo = "baz";
echo $bar; // outputs 'baz'
But yeah, take a look at the PHP symbol reference.
As for call by value/reference - the primary difference between the two is whether or not you're able to modify the original items that were used to call the function. See:
function increment_value($y) {
$y++;
echo $y;
}
function increment_reference(&$y) {
$y++;
echo $y;
}
$x = 1;
increment_value($x); // prints '2'
echo $x; // prints '1'
increment_reference($x); // prints '2'
echo $x; // prints '2'
Notice how the value of $x isn't changed by increment_value(), but is changed by increment_reference().
As demonstrated here, whether call-by-value or call-by-reference is used depends on the definition of the function being called; the default when declaring your own functions is call-by-value (but you can specify call-by-reference via the & sigil).
Let's define a function:
function f($a) {
$a++;
echo "inside function: " . $a;
}
Now let's try calling it by value(normally we do this):
$x = 1;
f($x);
echo "outside function: " . $x;
//inside function: 2
//outside function: 1
Now let's re-define the function to pass variable by reference:
function f(&$a) {
$a++;
echo "inside function: " . $a;
}
and calling it again.
$x = 1;
f($x);
echo "outside function: " . $x;
//inside function: 2
//outside function: 2
You can pass a variable by reference to a function so the function can modify the variable. More info here.
Call by value: Passing the variable value directly and it will not affect any global variable.
Call by reference: Passing the address of a variable and it will affect the variable.
Call by value means passing the value directly to a function. The called function uses the value in a local variable; any changes to it do not affect the source variable.
Call by reference means passing the address of a variable where the actual value is stored. The called function uses the value stored in the passed address; any changes to it do affect the source variable.
It means $($a), so its the same as $name (Since $a = 'name'). More explanation here What does $$ (dollar dollar or double dollar) mean in PHP?
